With the technology development and the growing demands for mobile devices, the demand for secondary batteries as an energy source is dramatically increasing, and among secondary batteries, lithium secondary batteries with high energy density and discharge voltage have been studied extensively and are being widely used in the commercial industries. Moreover, with the accelerated development of electric vehicle such as hybrid vehicle to solve the environmental problem caused by automobile exhaust gas, studies on the use of lithium secondary batteries as an automobile power source are also making a fast progress.
A lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution, and by the intercalation of lithium ions from a positive electrode active material to a negative electrode active material, for example, carbon particles, during first charge and deintercalation for discharge, also known as energy transfer between the two electrodes, the lithium secondary battery can be charged and discharged.
The positive electrode active material used in the lithium secondary battery includes lithium cobalt composite oxide, lithium nickel composite oxide, and lithium manganese composite oxide, and among them, lithium manganese composite oxide is gaining attention due to the use of manganese of rich resources and low costs as a main raw material.
However, manganese-based lithium secondary batteries using lithium manganese composite oxide as a positive electrode active material have a problem with the release of manganese into an electrolyte solution during charging and discharging processes, causing battery degradation. The release of manganese substance becomes more serious when stored at high temperature, and when the released manganese substance is precipitated on the surface of a negative electrode active material, for example, a carbon material, the electrolyte solution decomposes fast in the negative electrode active material by a reduction reaction with electrons from the negative electrode active material, accompanied by an increase in resistance of the battery. This problem causes a serious deterioration in output (power), and is an obstruction to development of high-performance (high-output) manganese-based lithium secondary batteries.
Accordingly, in the lithium secondary batteries using a manganese-based positive electrode active material, there is an urgent need for lithium secondary batteries with improved high-temperature stability to improve high-temperature storage characteristics and high-temperature cycle characteristics.